Understanding the anomalously long duration time of the transmitted pulse from a soft specimen in a kolsky bar experiment

Abstract

The reason for the observation of an anomalously long pulse duration time of a signal transmitted from a soft specimen in a Kolsky bar experiment is investigated. A systematic numerical experiment based on explicit finite element analysis has been carried out using elastic specimens with varying elastic moduli. The soft specimen is in a compressive state even after the passage of the pulse because it cannot push the bars, such that a fairly long transmitted pulse is monitored at the gage position of the output bar. The arrival of the second pulse (tensile) from the right-end surface of the output bar releases the first transmitted signal (compressive) coming from the compressed state of the specimen, which puts an end to the fairly long transmitted pulse. Because the observation of a prolonged transmitted pulse is a natural phenomenon, the prolonged transmitted pulse should not annoy researchers in the process of confirming the validity of experiments on soft specimens. Our concern in verifying the validity of experiments can be limited to other aspects such as the process of measurement and the amplification of weak transmitted signals coming from soft specimens.

Design guidelines for the striker and transfer flange of a split Hopkinson tension bar and the origin of spurious waves

“…From the viewpoint of obtaining accurate SHB test results, this situation is analogous to the case in which an anomalously long transmitted pulse is measured in compressive SHB tests on a soft specimen. 14 Because a long transmitted pulse is a natural phenomenon in tests on soft specimens and it does not influence the transmitted pulse within the time window, the long transmitted pulse can be used safely for signal processing. 14…”

“…14 Because a long transmitted pulse is a natural phenomenon in tests on soft specimens and it does not influence the transmitted pulse within the time window, the long transmitted pulse can be used safely for signal processing. 14…”

“…Split Hopkinson bars (SHBs) 1–9 are being used extensively to measure the uniaxial stress–strain and strain rate–strain curves of various solids 10–16 at high strain rates. These measured curves are generally used to calibrate a strain rate-dependent constitutive model, 17–24 which is indispensable for computer simulations of the deformation behaviour of solids and structures at high strain rates.…”

Minimum Required Distance of Strain Gauge from Specimen for Measuring Transmitted Signal in Split Hopkinson Pressure Bar Test

“…The extracted signals in the numerical simulation were processed through a one-dimensional analysis [7][8][9][10][11]:…”

“…Stress-strain curves measured under the uniaxial stress condition at a wide range of strain rates are required for the calibration of a strain-rate-dependent constitutive equation. Pseudo-onedimensional impact systems such as the split Hopkinson bar (SHB) [7][8][9][10][11] and the direct impact bar (DIB) [12][13][14][15][16] are widely used for measuring the uniaxial stressstrain curves of various materials at strain rates of approximately 10 2 -10 4 s -1 and over 10 4 s -1 , respectively.…”